Coated packaging material

ABSTRACT

A WAX COATED PACKAGING SHEET MATERIAL IS PROVIDED WITH IMPROVED SEPARATING CHARACTERISTICS BY APPLYING TO THE WAX SURFACE OF A PACKAGING SHEET MATERIAL A HOMOGENEOUS MIXTURE OF AN AMIDE AND STARCH IN A PARTICULAR AMOUNT. THE AMIDE HAS A MOLECULAR WEIGHT OF AT LEAST 200 AND PREFERABLY HAS A MOLECULAR WEIGHT IN THE RANGE OF FROM ABOUT 1,000 TO ABOUT 50,000. THE AMIDE COMPRISES THE LARGER AMOUNT OF THE MIXTURE AND THE STARCH COMPRISES A MINOR AMOUNT OF THE MIXTURE.

United States Patent thee 3,598,634 Patented Aug. 10, 1971 3,598,634 COATED PACKAGING MATERIAL John H. Kraft, Skokie, Ill., assignor to Kraftco Corporation, New York, N .Y. No Drawing. Filed Nov. 5, 1968, Ser. No. 773,649

Int. Cl. B32b 23/04 US. Cl. 11786 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to improvements in wax coated packaging sheets, and more particularly relates to improvements in the separation properties of wax coated packaging sheets.

Wax coated packaging sheets are well known to the packaging art. Such packaging materials have been used particularly to package food materials, such as cheese, bread, luncheon meats and processed vegetables and fruits. Generally, in the preparation of wax coated packaging sheets, a suitable base sheet is selected and is coated with molten wax. By base sheets is meant various sheet materials, such as paper, foil, and various plastics which have been found suitable in preparing wax-coated sheets. The term wax refers to any of the various waxy materials which have been found suitable in preparing packaging materials. These include paraffin, carnauba and various micro-crystalline waxes.

Wax coated packaging sheets are generally prepared by means of high speed equipment. A roll of the base sheet is unwound and a melt of the wax is applied to one surface of the base sheet. The wax coated base sheet may then be cooled to set the wax, and the wax-coated base sheet is then rewound upon a take-up roll. A major problem in the preparation and use of the wax-coated packaging sheet is their tendency to block, that is, to resist separation by a separating force applied perpendicular to the film, such as by a simple lifting action. Wax-coated packaging sheets also exhibit poor slip, that is, they do not slide readily over each other. The poor blocking and slip behavior of wax-coated packaging sheets results in poor handling characteristics and interferes with their use in automatic processing equipment.

It has been proposed to reduce the blocking of waxcoated packaging sheets by applying a layer of starch to the wax surface of the packaging material upon a roll. The application of starch to the wax surface to prevent blocking is not completely satisfactory in that relatively heavy coatings of starch must be used before the desired non-blocking effect is achieved. When it is desired to effect a subsequent seal of the packaging material, the starch must be displaced by pressure and the wax must flow over the starch to effect a good seal. This sometimes results in the use of heavier coatings of wax then are necessary to provide the packaging material with the desired physical properties.

It would be desirable to provide wax-coated packaging sheet material with improved separating characteristics. It would also be desirable to provide block-resistant waxcoated packaging sheet materials which can be readily sealed.

Accordingly, it is a principal object of the present invention to provide improved wax-coated packaging sheet material. It is another object of the present invention to provide wax-coated packaging sheet material with improved separating characteristics. It is a further object of the present invention to provide wax-coated packaging sheet materials with non-blocking characteristics and with good sealing properties.

These and other objects of the invention will become more clear from the following detailed description.

Generally, it has been found that the separating characteristics of wax-coated packaging sheet material can be improved and good sealing properties retained by applying to the wax surface of a packaging sheet material a homogeneous mixture of a high molecular weight amide and starch in a particular amount. More particularly, the amide has a molecular weight of at least 200 and preferably has a molecular weight in the range of from about 1,000 to about 50,000. The amide comprises a major amount of the mixture and the starch comprises a minor amount of the mixture. The mixture may be applied to the surface of the wax coating of the packaging sheet material by various methods known to those skilled in the art.

The amide of the invention may be an amide of a higher fatty acid. The term amide of a higher fatty acid is intended to include amides of saturated and unsaturated, water-insoluble monocarboxylic acids and particularly t-hose higher fatty acids having at least 12 carbon atoms in the chain. Such higher amides include the amides of oleic acid, arachidic acid, behenic acid and erucic acid. It is particularly preferred, however, to use amides having molecular weights in excess of about 1,000, which are prepared from the reaction of diamines and polymerized fatty acids which are formed by polymerization at the double bond position in unsaturated higher fatty acids. The polymerized acids are desirably di-carboxylic, and the amides formed by the reaction of the dicarboxylic acids and diamines are referred to herein as polyamides.

Polyamides are readily prepared by heating a mixture of the di-carboxylic polymerized acids and the diamine at a predetermined temperature, and thereafter removing the water of formation. Such polyamides are commercially available in various grades under the trade names Versamid and Milvex, sold by General Mills, Inc. The amide of higher fatty acid may be in a suitable carrier, such as propyl alcohol.

The starch of the mixture may be any of various plant starches. Preferred starches are those obtained from corn, potato or rice. The starch is preferably nongelatinized and is dry. As will be described more fully hereafter, the mixture of the invention is usually applied to the wax surface of a wax-coated packaging sheet material from a fluid dispersion of the amide and the starch. Therefore, it is preferred to use a starch that has a particle size sufficiently small that settling of the starch in the dispersion is not a problem. Specifically, it is preferred to use starches which have a particle size of at least less than about 60 mesh. As indicated above, the amide is present in the homogeneous mixture in a major amount, and preferably comprises from about 50 to about percent by weight of the mixture. The starch preferably comprises from about 10 to about 50 percent of the mixture.

The mixture is applied to the packaging material at levels suflicient to provide from about 0.1 to about 1.5 pounds of the mixture per 3,000 square feet of the packaging material. The mixture tends to provide a coating on the wax and it must not be so thick as to interfere with sealing but must be thick enough to provide the desired separating properties. It has been found that the 3 indicated range provides adequate separating properties while permitting good seals.

When the composition of the present invention is used on wax coated packaging sheet materials, the level of wax may be reduced from that previously used with other particular anti-blocking materials. For example, starch is known as an anti-blocking material when used by itself. However, when starch is applied to a wax coated packaging sheet material, the level of wax must be substantially above that used when the present composition is used.

While not wishing to be bound by any theory, it is believed that the composition of the present invention provides a coating which is more easily fractured during sealing of a package so that the wax can function to effect a seal. When starch alone is used, a substantially higher level of starch must be used to provide separating characteristics. When a seal is to be effected in the packaging material, the starch which covers the wax must be pressed and the wax melted so as to flow through the starch in the region of the seal. It has been found that the amide of higher fatty acid when used alone does not provide adequate anti-blocking properties. When the composition of the present invention is used at the indicated level on the same material, there is adequate provision of separating properties and effective seals can be achieved.

While the composition of the invention may be used with many Wax-coated packaging sheet materials, it is particularly adapted for use with wax coated packaging sheet material regularly used in the packaging of cheese. A particularly suitable packaging sheet material is one wherein the base sheet is a polymer coated cellophane to which is applied a micro-crystalline wax fortified with polyisobutylene or comminuted butyl rubber. When the composition of the present invention is applied to the wax surface of such packaging sheet material, the Wax coating may be in the range of from about 35 to about 50 pounds of wax per 3,000 square feet of packaging sheet material. As previously indicated, the composition of the invention is provided at a level of from about 0.1 to about 1.5 pounds of the composition per 3,000 square feet of the packaging material.

When starch alone is used as a coating for such wax coated packaging sheet material, the starch is applied at a level of form about 4 to about 5 pounds per 3,000 square feet of packaging material. Also, when starch alone is used as the coating material, the wax must usually be applied at a level of from about 45 to about 60 pounds per 3,000 square feet of packaging material. Also, the composition of the present invention provides better slip than is provided by the use of the starch alone or a polyamide alone.

The composition of the invention may be applied to the wax coated packaging sheet material by any suitable method. A preferred method is to disperse the amide and the starch in a suitable fluid carrier and to spray, dip coat, roll on or otherwise apply the dispersion to the surface of the wax coating of the sheet. The carrier is then removed by a subsequent drying step. Preferred carriers are organic fluids which are capable of dissolving the amide and are not reactive with the wax coating. Such carriers include, but are not limited to, short chain alcohols, such as ethyl, butyl or propyl alcohol. The starch may be moistened prior to adding the carrier. However, for reasons of economy during the drying step, it is preferred that the starch be substantially dry. The mixture of amide and starch may be present in the carrier at a level of from about 5 to about 50 percent by weight.

The following example further illustrates various of the features of the invention, but is intended to in no way limit the scope of the invention, which is defined in the appended claims.

Example A mixture of 7.7 parts of an amide, 90 parts of n-propyl al oh l and 2.3 parts of y o n sta c is p pa ed Th 4 amide used is available commercially under the trade name Milvex 1000, from General Mills, Inc. The corn starch is ungelatinized, dry and has a particle size which is less than 60 mesh.

A rolled sheet of polymer coated cellophane is coated with a molten mixture of micro-crystalline wax and comminuted butyl rubber. The cellophane has a size designation of 250, which means 25,000 square inches per pound of cellophane. The wax is applied at a level sufficient to provide 40 pounds of wax per 3,000 square feet of the polymer coated cellophane. The wax is applied by means of a gravure cylinder which revolves into a bath of the molten wax mixture and deposits a coating of wax onto the surface of the cellophane sheet.

The polymer coated cellophane sheet containing the coating of wax is then cooled to harden the wax and is passed by means of rolls to a second gravure cylinder. The second gravure cylinder revolves through a bath of the amide-starch mixture. The amide-starch mixture is applied to the wax surface at a level sufiicient to provide 0.5 pound of the amide-starch mixture on a solid basis per 3,000 square feet of the wax-coated cellophane. The alcohol is then removed by passing the sheet through a dryer. The sheet of polymer coated cellophane, containing a wax coating and an amide-starch coating, is then wound upon a take-up roll.

When the packaging sheet material is removed from the roll, it is found that easy separation is effected between each layer of packaging material on the roll.

The sheet material is used to wrap hot or cold cheese and is readily sealed. The sheet material also has good separating properties from cheese when packaged hot.

What is claimed is:

1. An improved wax coated packaging sheet material comprising a base sheet, a wax coating and a coating applied to the wax coating which has separating properties, said separating coating consisting essentially of a mixture of a major amount of an amide of a higher fatty acid and a minor amount of a starch, said amide having a molecular weight of above at least 200, said separating coating being at a level which permits heat sealing of the sheet material.

2. An improved wax coated packaging sheet material in according with claim 1 wherein said amide has a molecular weight of-from between about 1,000 and about 50,000.

3. An improved wax coated packaging sheet material in accordance with claim 1 wherein said starch is selected from corn starch, potato starch or rice starch, said starch having a particle size of less than about 60 mesh.

4. An improved wax coated packaging sheet material in accordance with claim 1 wherein said base sheet is polymer coated cellophane, the wax is a microcrystalline wax, said amide is derived from the reaction of polymerized unsaturated vegetable oils and ethylene diamine.

5. An improved wax coated packaging sheet material in accordance with claim 1 wherein said separating coating contains from about 50 to about percent by weight of said amide and from about 10 to about 50 percent by weight of said starch.

6. An improved wax coated packaging sheet material in accordance with claim 1 wherein said separating coating is present at a level of from about 0.1 to about 1.5 pounds per 3,000 square feet of said packaging sheet material.

References Cited UNITED STATES PATENTS 2,833,671 5/1958 Funk et al 1l7-86X 3,355,348 11/1967 Lamar 117--7 6(P)X 3,458,346 7/1969 Mitchell et al 1l776(P) WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. Cl. X.-R. 

